The present invention pertains to nuclear reactors and, more particularly, to a method of safely removing in-core instruments and SRM/IRM dry tubes from a boiling water reactor (BWR) during a refueling outage.
In-core instruments and dry tubes are commonly replaced during refueling outages of boiling water reactors. The used instruments and tubes are removed from the reactor vessel and scrapped. Since they have become radioactive, they must at all times during removal be kept beneath at least a certain amount of shielding water. This shielding requirement is especially important with respect to the in-core portions, approximately the upper 15 feet, of the instruments and tubes. Removal is further complicated by the extreme length of the items, approximately 42 feet, and space limitations within the reactor cavity.
Present removal methods involve bending the instruments and tubes double, or dragging them at an angle, so that they may be removed to an adjacent, water-filled equipment pool where they are cut into sections of a more convenient length. These methods are time consuming. Further, dragging members through the reactor vessel may create contamination problems.
It is, therefore, an object of the present invention to provide a safe and convenient method of removing excessively lengthy members, such as in-core instruments and dry tubes, from a boiling water reactor during a refueling outage.
The foregoing and other objects and advantages as may hereinafter appear are achieved by a method wherein a temporary storage container is provided within the reactor cavity, preferably within the reactor core, having a remotely operated cutting device superposed thereon. The elongate member is suspended by an end, with the in-core part uppermost, above the temporary storage container and lowered until a portion of the member is within the container. The cutting device is then operated to sever the portion of the member within the container. The steps, of lowering a portion of the elongate member into the temporary storage container and of then severing that portion, are repeated a desired number of times until all of the out-of-core part of the member is in the temporary container. The temporary storage container and the in-core part of the elongate member may now be removed from the reactor cavity in the manner conventionally utilized for items with these radioactivity levels.
Preferably, a second temporary storage container is provided, proximate the first one, into which the in-core part of the elongate member may be lowered. Removal of the in-core part of the member is then effected by removing the second temporary storage container.